浮点数比较中的问题以及如何正确比较？
在本文中，我们将了解比较浮点数的问题，并讨论比较两个浮点数的正确方法。 通常比较浮点数有什么问题？ 我们先借助 关系运算符(==) 比较两个浮点数。 示例:使用“==”进行比较
卡片打印处理机（Card Print Processor 的缩写）
// C++ program to compare
// floating point numbers
#include <bits/stdc++.h>
using namespace std;
void compareFloatNum(double a, double b)
{
if (a == b) {
cout << "The numbers are equal"
<< endl;
}
else {
cout << "The numbers are not equal"
<< endl;
}
}
// Driver code
int main()
{
double a = (0.3 * 3) + 0.1;
double b = 1;
compareFloatNum(a, b);
}
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to compare
// floating point numbers
class GFG
{
static void compareFloatNum(double a, double b)
{
if (a == b)
{
System.out.print("The numbers are equal" + "\n");
}
else
{
System.out.print("The numbers are not equal" + "\n");
}
}
// Driver code
public static void main(String[] args)
{
double a = (0.3 * 3) + 0.1;
double b = 1;
compareFloatNum(a, b);
}
}
// This code is contributed by 29AjayKumar
计算机编程语言
# Python program to compare
# floating point numbers
def compareFloatNum(a, b):
if (a == b):
print("The numbers are equal")
else:
print("The numbers are not equal")
# Driver code
a = (0.3 * 3) + 0.1
b = 1
compareFloatNum(a, b)
# This code is contributed by mohit kumar 29
C
// C# program to compare
// floating point numbers
using System;
class GFG
{
static void comparefloatNum(double a, double b)
{
if (a == b)
{
Console.Write("The numbers are equal" + "\n");
}
else
{
Console.Write("The numbers are not equal" + "\n");
}
}
// Driver code
public static void Main(String[] args)
{
double a = (0.3 * 3) + 0.1;
double b = 1;
comparefloatNum(a, b);
}
}
// This code is contributed by PrinciRaj1992
java 描述语言
<script>
function compareFloatNum(a,b)
{
if (a == b)
{
document.write("The numbers are equal" + "<br>");
}
else
{
document.write("The numbers are not equal" + "<br>");
}
}
let a = (0.3 * 3) + 0.1;
let b = 1;
compareFloatNum(a, b);
// This code is contributed by patel2127
</script>
Output:
The numbers are not equal
为什么会出现这个问题？ 在浮点数的情况下， 关系运算符(==) 不会产生正确的输出，这是由于浮点数舍入时的内部精度错误。 在上面的例子中，我们可以看到使用“==”运算符比较两个浮点数的不准确性。两个数字“a”和“b”相等(如(0.3 * 3) + 0.1 = 1)，但程序导致不正确的输出。 让我们仔细看看下一个片段中的数字。
卡片打印处理机（Card Print Processor 的缩写）
// C++ program to compare
// floating point numbers
#include <bits/stdc++.h>
using namespace std;
void printFloatNum(double a, double b)
{
// To print decimal numbers up to 20 digits
cout << setprecision(20);
cout << "a is : " << a << endl;
cout << "b is : " << b << endl;
}
// Driver code
int main()
{
double a = (0.3 * 3) + 0.1;
double b = 1;
printFloatNum(a, b);
}
Python 3
# Python 3 program to compare
# floating point numbers
def printFloatNum(a, b):
# To print decimal numbers up to 20 digits
print("a is : %.20f" %a)
print("b is : %.20f" %b)
# Driver code
if __name__ == "__main__":
a = (0.3 * 3) + 0.1
b = 1
printFloatNum(a, b)
# This code is contributed by ukasp.
Output:
a is : 0.99999999999999988898
b is : 1
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